Developments over the last twenty to thirty years in science and industry have promoted the keeping of animals in racks of cages. These animals are primarily small mammals such as rabbits, rats, hamsters, guinea pigs, and mice.
Due to the distinctive demands of laboratory work, cages have been further specialized so that they provide for the animal's comfort, are easily cleaned and sterilized, and/or may be uniformly positioned on storage racks to provide the maximum number of cages in the available space while maintaining adequate ventilation and spacing necessary to prevent the spread of disease.
In the prior art, it was believed that the most common way to prevent the spread of disease through contact of the animals while insuring adequate ventilation was to design the cage with an open or a solid top, three solid side walls, and an open grated front wall. The bottom was an open grid that permitted waste material to pass onto the collection tray below. Nevertheless, it has been discovered that these types of cages do not prevent the spread of disease as airborne pathogens could easily pass from one cage to another in the rack, thereby permitting the quick transmission of pathogens from animals in adjacent cages. These open-topped cages did offer certain advantages. For example, open topped hanging cages that slide into brackets mounted on the underside of shelves on the racks have the advantage that they do not require doors since the underside of the shelf serves as a solid barrier (or top) for the animal cage and access to the cage is easily provided by sliding the cage out from the rack to expose the open top. This permits the food and water containers to be directly mounted on the front, open grated panel for maximum utilization of area at a minimum cost.
Another drawback to these cages is that, due to economic considerations, they are constructed out of a single sheet of metal to which a grid is attached at the front and on the bottom. Not only do the cages not come apart for storage, but they may only be used for one variety of animal, for example a rat, and not another animal of a different size, for example a mouse. The mouse could escape through or be injured by the larger grid used for containing a rat, and the waste material of the larger animal, the rat, would not go through the smaller grid used for a mouse.
Other prior art cages include a cage bottom having four walls and a base with an open top. A wire bar lid that stretches across the top of the cage bottom and extends into the cage bottom, is disposed between the cage bottom and bonnet. A bonnet supporting an air filter thereon is placed on top of the cage bottom wire bar lid thereby covering the cage bottom. The wire bar lid is constructed from stainless steel and supports food and water in the cage while also preventing the rodents, particularly rats, from gnawing through the bonnet and damaging the filter or escaping from the cage.
Several problems exist with the use of the wire bar lid in the prior art cage design. First, because the wire bar lid extends into the cage bottom, it creates an artificial ceiling between the cage bottom and the bonnet thereby reducing the amount of area and height available for the rodents. Also the wire bar lid must be removed to provide access to the animal requiring labor and work space for placing the lid during use. Also, the wire bar lid prevents the bonnet from sitting flush on the cage bottom thereby allowing air to either escape or enter the cage bottom over the lid wires creating a Venturi effect in a ventilated cage environment. Although this problem is most pronounced when rounded wire bar lids are used, it nevertheless exists even when flat rimmed wire bar lids are employed.
In addition, some prior art cages have a drawback in that materials that are used to construct the cages are not capable of withstanding chemical and/or steam sterilization. Such cages are often sterilized in autoclaves at 120°-130° C. causing the cage to denigrate over time. This results in the drawback that with the passing of time the cage becomes opaque, prohibiting visualization of animals within the cage, or the cages become cracked and crazed preventing an adequate level of sanitation.
Accordingly, what is needed is a novel animal containment device that eliminates one or more of the disadvantages of prior art animal containment devices. In particular, the animal containment device may be used in ventilated racks, may be durable and able to withstand the rigors of sterilization, and/or may be designed to be easily monitored.